The use of load stabilizing devices or mechanisms in connection with forklift trucks, including lift trucks or hoist trucks, is well known. The load stabilizing apparatus is mounted in substantially superimposed relation over the forks or tines of the forklift truck, and the hydraulic system of the forklift truck is employed to operate a hydraulic piston and cylinder for vertical reciprocation of the stabilizer independently of vertical movement of the forks.
In operation, the load stabilizer is reciprocated to an upward position above the height of the load to be carried, and the tines of the truck are brought into position underneath the load, usually on a pallet. The stabilizer is then brought down into engagement with the top of the load so as to apply a clamping force to the same. Additionally, some load stabilizers include side clamping mechanisms which can be brought into engagement with the side of the load for further stabilization of the load as carried by the truck. The entire load may be lifted by the tines or forks, and the stabilizer will maintain the same clamping pressure on the load, regardless of the height to which the forks are lifted.
My prior U.S. Pat. No. 3,773,202 describes in detail an adjustable load stabilizer frame which may be advantageously employed to accommodate a very wide range of vertical height adjustments of the load stabilizer. In my prior patent a brief description of the load stabilizing clamping structure is set forth, although the details of construction of the clamping mechanism itself are incomplete, since they were not pertinent to the vertical adjustment apparatus of my prior invention.
In addition to the limited disclosure of my prior patent, the prior art includes load stabilizing mechanisms designed to engage and clamp the top of a single large container, such as the devices of U.S. Pat. Nos. 3,272,364 and 2,807,382. These devices are not well suited, for example, for gripping a plurality of small boxes, such as fruit or vegetable crates.
Some load stabilizers are simply formed as flat plates which can be brought into engagement with the top of a load, for example, the stabilizers U.S. Pat. Nos. 3,567,053 and 2,875,912, and the plate-like stabilizer set forth in the 1965 brochure of Little Giant Products Inc. for its LITTLE GIANT brand load stabilizer. This approach limits the degree to which the stabilizer can accommodate uneven top surfaces, usually to the depth of a foam pad or the like mounted on the plate or frame.
More complex forklift truck load stabilizing devices are shown in U.S. Pat. Nos. 3,133,655 and 3,024,929. These devices employ apparatus designed to engage the load at discrete, predetermined locations, which limits their use to specialized applications, again primarily to large boxes.
Perhaps the most versatile prior lift truck load stabilizing devices are those which employ a leaf spring top clamping structure. Typical of these devices are the stabilizer of U.S. Pat. No. 2,684,165 and the stabilizers described in the brochures of Equipment Sales Co. for its PHILIFT brand stabilizer and Edwards Equipment Company for its TRANS-FORK brand stabilizer. Even these devices, however, lack a side clamping capability, present a towing problem and are limited in the load configurations which they can accommodate.
Thus, various prior art load stabilizers are adequate if the forklift truck is used to carry only one kind of load, but when a stabilizer is to be used in general duty warehousing with loads of various configurations, such prior stabilizers have been found to have substantial disadvantages. They may not be able, for example, to accommodate load heights which vary across the length and width of the pallet. Often there is no provision for side clamping or adjustment of the width of the side clamping apparatus. Still further, some side clamping apparatus will not accommodate extremely wide loads. Moreover, there has been a problem with transport of load stabilizers when the forklift truck is being towed from site to site. Accordingly, the use of forklift truck load stabilizers has often been confined to specialized industries which have uniform and repetitive load configurations.